Robot cleaner, robot cleaning system and method for controlling the same

ABSTRACT

A robot cleaner, a robot cleaning system and a method for controlling the same capable of efficiently performing work on command by recognizing the driving distance and direction of the robot cleaner regardless of a of wheel slippage or irregularity in the floor. The robot cleaner performs a working operation while moving about a floor, and comprises a main body, a driving unit for driving a plurality of wheels disposed on a bottom portion of the main body, a downward-looking camera disposed among the wheels on the bottom portion of the main body for photographing images of the floor perpendicular to the driving direction of the robot cleaner, and a control unit for recognizing driving distance and direction of the wheels using image information of the floor photographed by the downward-looking camera, and for controlling the driving unit corresponding to a target work by using the recognized distance and direction of the wheels. An upward-looking camera can photograph and use information relating to spatial orientation for determining and correcting driving distance and direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a robot cleaner, a robotcleaning system and a method for controlling the same, and moreparticularly to a robot cleaner, a robot cleaning system and a methodfor controlling the same that is capable of recognizing driving distanceand direction to arrange a driving path by using image information of afloor photographed while the robot cleaner is driving around the floor.

2. Background of the Related Art

A conventional robot cleaner drives along an outline of a work area thatis surrounded by a wall or obstacle by using an ultrasonic sensorinstalled in a main body to determine the extent of the work area, andthen plans a driving path for its work, such as cleaning or securitywork, in the predetermined work area. The robot cleaner, then,calculates driving distance and current position by using a signaldetected by a sensor such as an encoder capable of detecting a numberand angle of rotation of wheels for driving the wheels to move along theplaned driving path. However, the above generally used method fordriving the robot cleaner along the driving path may produce errorsbetween the driving distance and position calculated from the signaldetected by the sensor and the actual driving distance and position dueto an irregularity of the floor, slip of the wheels, etc. The moredistance over which the robot cleaner drives, the more the positionrecognition errors may be accumulated. The accumulated position errorsmay accordingly cause the robot cleaner to deviate from the planneddriving path. Consequently, cleaning may not be performed for some ofthe predetermined area, or may be repeatedly performed for other areas,whereby cleaning efficiency can diminish and security work may not beperformed in some cases.

Accordingly, a necessity has risen for a robot cleaner capable ofefficiently performing commanded work by accurately detecting thedriving distance and direction to precisely arrange a driving pathregardless of slip of wheels, irregularity of the floor or some othererror producing event.

SUMMARY OF THE INVENTION

An object of the invention is to solve at least the above problemsand/or disadvantages and to provide a robot cleaner, robot cleaningsystem and method for controlling the same capable of efficientlyperforming commanded work by precisely recognizing the driving distanceand direction of the robot cleaner.

The foregoing objects and advantages are realized by providing a robotcleaner for performing working operations while moving about a floor,comprising: a main body; a driving unit for driving a plurality ofwheels disposed on a bottom portion of the main body; a downward-lookingcamera disposed among the wheels on the bottom portion of the main bodyfor photographing images of the floor perpendicular to the drivingdirection of the robot cleaner; and a control unit for recognizingdriving distance and direction of the wheels using image information ofthe floor photographed by the downward-looking camera, and forcontrolling the driving unit corresponding to the target work by usingthe recognized stored distance and direction of the wheels.

Preferably, the control unit compares the current image of the floorphotographed by the downward-looking camera with previous images of thefloor stored by the downward-looking camera so as to recognize thedriving distance and direction of the wheels. Here, it is preferablythat the downward-looking camera photographs images of the floor at arate of 1500 times per second.

Preferably, the robot cleaner further comprises an illuminator disposedon the bottom portion of the main body for illuminating an areaphotographed by the downward-looking camera so as to render it brighterthan surrounding areas.

According to another aspect of the invention, a robot cleaner forperforming working operations while moving about a floor, comprises: amain body; a driving unit for driving a plurality of wheels disposed ona bottom portion of the main body; a downward-looking camera disposedamong the wheels on the bottom of the main body for photographing imagesof the floor perpendicular to the driving direction of the robotcleaner; an upward-looking camera disposed on a top of the main body forphotographing images of a ceiling perpendicular to the drivingdirection; and a control unit for recognizing the position of the robotcleaner by using image information of the ceiling photographed by theupward-looking camera and for recognizing a driving distance anddirection of the wheels by using image information of the floorphotographed by the downward-looking camera, and further for controllingthe driving unit corresponding to a target work by using the recognizedposition, distance and direction.

Here, the control unit compares the current image of the floorphotographed by the downward-looking camera with previous images of thefloor stored by the downward-looking camera to recognize the drivingdistance and direction of the wheels.

The foregoing objects and advantages are further realized by providing arobot cleaning system comprising: a robot cleaner including: a mainbody, a driving unit for driving a plurality of wheels disposed on abottom portion of the main body, and an upward-looking camera disposedon a top of the main body for photographing images of a ceilingperpendicular to a direction of driving the robot cleaner; and a remotecontrol unit for communicating wirelessly with the robot cleaner,wherein the robot cleaner further includes a downward-looking cameradisposed among the wheels on the bottom portion of the main body forcontinuously photographing images of the floor perpendicular to thedriving direction, and the remote control unit recognizes a drivingdistance and direction of the wheels by using image information of thefloor photographed by the downward-looking camera and controls thedriving unit corresponding to the targeted work by using the recognizeddistance and direction of the wheels.

Here, the remote control unit compares the current image of the floorphotographed by the downward-looking camera with previous images of thefloor stored by the downward-looking camera so as to recognize thedriving distance and direction of the wheels.

Preferably, the robot cleaning system further comprises an illuminatordisposed on the bottom of the main body for illuminating an areaphotographed by the downward camera brighter than surrounding areas.

The foregoing object and advantage are further realized by providing amethod for controlling a robot cleaner having a downward camera,comprising the steps of: calculating a driving path to a target areacorresponding to a work, upon receiving a work command; storing imagesof a floor photographed by the downward camera; driving the robotcleaner along the calculated driving path; and comparing a current imageof the floor photographed by the downward camera with the stored imagesto calculate a driving distance and direction, and arranging the drivingpath.

With the above described robot cleaner, robot cleaning system and methodfor controlling the same, the driving distance and direction of therobot cleaner are recognized by using the images of the floorphotographed by the downward camera to arrange the driving path, therebycapable of efficiently performing the commanded work.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objects and advantages of the invention may be realizedand attained as particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in detail with reference to the drawingsin which like reference numerals refer to like elements wherein:

FIG. 1 is an elavational view showing a robot cleaner used forphotographing images of a floor while moving thereabout in accordancewith the invention;

FIG. 2 a is a perspective view showing the bottom portion of the robotcleaner of FIG. 1;

FIG. 2 b is a perspective view showing the robot cleaner of FIG. 1 withthe upper cover separated therefrom;

FIG. 3 is a schematic block diagram showing a robot cleaning system inaccordance with the invention;

FIG. 4 a is a top view showing an image of the floor photographed by adownward camera of the robot cleaner of FIG. 1 while standing still;

FIG. 4 b is a top view showing an image of the floor photographed by thedownward camera of the robot cleaner while moving forward from the statein FIG. 4 a;

FIG. 4 c is a top view showing an image of the floor photographed by thedownward camera of the robot cleaner while moving backward from thestate in FIG. 4 a;

FIG. 4 d is a top view showing an image of the floor photographed by thedownward camera of the robot cleaner while moving to a right from thestate in FIG. 4 a;

FIG. 4 e is a top view showing an image of the floor photographed by thedownward camera of the robot cleaner while moving to a left from thestate of FIG. 4 a;

FIG. 4 f is a top view showing an image of the floor photographed by thedownward camera of the robot cleaner while moving at about 45 degreeangle to the left from the state in FIG. 4 a;

FIG. 5 is a block diagram of the CCU (Central Control Unit) shown inFIG. 3; and

FIG. 6 is a flow chart showing the working process of the robot cleanerin accordance with the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The preferred embodiments of the invention will be hereinafter describedin detail with reference to the accompanying drawings.

Referring to FIGS. 1, 2A and 2B, a robot cleaner 10 is provided with amain body 12, a suction unit 16, a driving unit 20, an upward-lookingcamera 30, a forward-looking camera 32, obstacle detection sensors 34, adownward-looking camera 50, an illuminator 55, a control unit 40, amemory 41 and a transmitter/receiver unit 43. The power source maycomprise a stored electrical source, such as battery 14.

The suction unit 16 is installed on the main body 12 in order to collectdust on a surface, such as a floor, to be cleaned while drawing in air.The suction unit 16 can be constructed using well-known methods. Thesuction unit 16, as an example, may have a suction motor (not shown),and a suction chamber, for collecting dust drawn in through a suctionhole or a suction pipe formed on, for example, the underside of the body12, opposite to the floor to be cleaned, by driving of the suctionmotor.

The driving unit 20 comprises two wheels 21 a, 21 b disposed at bothsides of the front of the body 12, two wheels 22 a, 22 b disposed atboth sides of the back of the body 12, motors 23, 24 for rotatablydriving the back wheels respectively and timing belts 25 fortransmitting power generated to the back wheels 22 a, 22 b by the motors23, 24 to the front wheels 21 a, 21 b. The driving unit 20 rotatablydrives the motors 23, 24 respectively in a forward or reverse directionin accordance with control signals received from the control unit 40.The driving direction of the robot 10 can be determined by controllingthe motors 23, 24 to have different amounts of rotation.

The forward-looking camera 32 is installed on the main body 12 in orderto photograph front images looking in a forward direction. Theforward-looking camera 32 outputs the photographed images to the controlunit 40.

The upward-looking camera 30 is disposed on the main body 12 in order tophotograph upper images of a ceiling in an upward-looking direction. Theupward-looking camera 30 outputs the photographed images to the controlunit 40. Preferably, the upward-looking camera comprises a fisheye lens(not shown).

Fisheye lenses have at least one lens designed to provide a wide viewangle to the camera, similar to the eyes of a fish, for example, and maygenerate an image up to about 180 degrees. The fisheye lens is designedto fit to a required range of view angles while including an allowabledistortion. A detailed description of the fisheye lens will be omittedhere. However, such a fisheye lens is disclosed in Korean Patents Nos.1996-7005245, 1997-48669, 1994-22112, etc., and is available fromvarious lens makers.

The obstacle detection sensors 34 ate disposed around a cylindrical sidewall of the body at predetermined intervals, and are provided fortransmitting signals externally of the body 12 and receiving thereflected signals. Each of the obstacle detection sensors 34 has aplurality of infrared ray luminous elements 34 a for projecting infraredrays and light-receiving elements 34 b for receiving reflected infraredrays. The infrared ray luminous elements 34 a and light-receivingelements 34 b are disposed along an outer circumference of each of theobstacle detection sensors 34 by perpendicularly arranged pairs. Theobstacle detection sensors 34 may also adopt an ultrasonic sensorcapable of projecting ultrasound and receiving a reflected ultrasoundvibration. The obstacle detection sensors 34 may be used for measuringthe distance between the robot cleaner and an obstacle or an adjacentwall.

The downward-looking camera 50 is disposed on the main body 12 in orderto photograph images of the floor in a downward-looking direction. Thedownward-looking camera 50 outputs the photographed images to thecontrol unit 40. The downward-looking camera 50 is capable ofphotographing images at high speeds for rapid and precise recognition ofthe driving path of the robot. Preferably, a downward-looking cameracapable of photographing about 1500 times per a second may be used.

The illuminator 55 is disposed around the downward-looking cameradisposed under the main body 12 for illuminating an area in the floorphotographed by the downward-looking camera 50. The illuminator 55constantly illuminates the area photographed by the downward-lookingcamera so as to make it brighter than the surrounding areas. Theilluminator 55 enables the downward-looking camera to detect minordifferences in the floor and minimizes the changes in the photographedimages due to surrounding illumination.

The control unit 40 processes received signals through thetransmitter/receiver unit 43. In case the main body 12 further comprisesa key input device (not shown), having a plurality of keys so that auser can manipulate the keys to set functions, the control unit 40 mayprocess an input key signal from the key input device.

Referring now to FIGS. 1, 2A, 2B and 3, the memory 41 stores the upperand lower images photographed respectively by the upward-looking camera30 and downward-looking camera 50, and assists the control unit 40 incalculating position or driving information.

The transmitter/receiver unit 43 sends data through an antenna 42, andtransmits a signal received through the antenna 42 to the control unit40.

A method for controlling the robot cleaner having the above-describedconstruction by the control unit will be described hereinafter.

The control unit 40 recognizes the current position of the robot byusing the known position information of specific objects, such asdirect-light fluorescent lamps or fire alarms, evident in the upperimages of a ceiling of a work area photographed by the upward-lookingcamera, or by using position information of marks installed on theceiling of the work area for position recognition. The memory 41 storesthe standard image information of the specific objects for comparison orthe marks for position recognition to allow the control unit 40 torecognize the specific object or marks among the images photographed bythe upward-looking camera 30. The control unit 40 then calculates adriving path to perform the target work by using the recognized positioninformation and transmits control signals to each part to drive therobot cleaner 10 along the desired driving path.

The control unit 40 recognizes the driving distance and direction of therobot cleaner 10 by using special features, such as spots in the imagesof the floor, photographed by the downward-looking camera 50, anddetermines whether the robot cleaner 10 should move along the drivingpath by using the recognized driving distance and direction, and therebycontrols the driving unit 20 to drive the robot cleaner to follow thedriving path and not to deviate from the driving path.

Namely, the control unit 40 recognizes position changes of the specialfeatures, such as spots, in images by comparing a current image of thefloor 15 photographed by the downward-looking camera 50 with an image ofthe floor 15 photographed before the current image by the downwardcamera 50, which is stored in the memory 41. The control unit 40,thereafter, calculates the driving distance and direction of the robotcleaner 10 by using the position changes of the special features. Here,all patterns on the floor are different even though some patterns may beseen by human eyes as having the same patterns, because thedownward-looking camera 50 can recognize minor differences in thepatterns. Thus, there are special features, such as spots andcut-grooves, that cannot easily be seen by human eyes, but can berecognized by the downward-looking camera 50.

Various known methods may be adopted for image processing methods ofextracting special features from the photographed images. For example, amethod can be adopted which distinguishes pixel points from otherneighboring points, after converting the photographed image into a graylevel.

FIGS. 4 a to 4 f show relationships between the extracted specialfeatures and driving directions of the robot cleaner 10. FIG. 4 a is animage 52 of the floor photographed by the downward-looking camera 50 ata certain point while the robot cleaner 10 is stopped or moving. Here, areference mark P is the special feature extracted from the imagephotographed by the downward-looking camera 50. The special feature P inthe image of the floor moves relatively backwards, as shown in FIG. 4 b,when the robot cleaner 10 moves forward, while the special feature Pmoves forward as shown in FIG. 4 c when the robot cleaner 10 movesbackwards. Further, the special feature P in the image of the floormoves to the left, as shown in FIG. 4 d, when the robot cleaner 10 movesto the right, while the special feature P moves to the right, as shownin FIG. 4 e, when the robot cleaner 10 moves to the left. Furthermore,the special feature P moves at about a 45 degree angle to the right, asshown in FIG. 4 f, when the robot cleaner 10 moves at about a 45 degreeangle to the left.

When the downward-looking camera 50 continuously photographs the floor,the special feature P continuously changes positions in the photographedimages as shown above. The control unit 40 can then determine thedriving distance and direction of the robot cleaner 10 from the positionchanges of the special feature P. Thereafter, the control unit 40determines whether the robot cleaner 10 has followed the calculateddriving path, and, if the robot cleaner 10 deviated from the calculateddriving path, the control unit 40 controls the driving unit 20 to drivethe robot cleaner 10 to change the current driving path so as to followthe calculated driving path.

An operation of the control unit 40 will be described hereinafter forcontrolling the driving unit 20 through the upward-looking camera 30 anddownward-looking camera 50.

The control unit 40 recognizes a current position of the robot cleaner10 by comparing special features or marks for recognition in a currentimage inputted by the upward-looking camera 30 with the stored specialfeatures and marks for recognition, upon receiving a work command signalfrom the key input device or from the outside wirelessly, and thencontrols the driving unit 20 corresponding to a target driving path fromthe recognized position. Here, the work command signal may include acommand for cleaning the floor or security work through the cameras.

The control unit 40 calculates a driving error by using the drivingdistance and direction measured by the downward-looking camera 50 andthe current position recognized by comparing the currently photographedupper image with the previously photographed upper images stored in thememory 41, and controls the driving unit 20 to track the target drivingpath by compensating for the calculated driving error.

The above description provides an example by which the control unit 20can independently recognize the position of the robot cleaner 10 bydirectly using image information photographed by the upward-lookingcamera 30 and downward-looking camera 50.

According to another aspect of the invention, a robot cleaning system isprovided which may process calculations required to recognize a positionof a robot cleaner 10 externally, in order to reduce the calculationload for the position recognition of the robot cleaner 10.

Referring to FIG. 3, the robot cleaner 10 is configured to wirelesslysend information regarding the photographed image externally, andfurther to operate in response to a control signal received from theexternal command center. A remote controller 60 is provided towirelessly control the driving of the robot cleaner 10. The remotecontroller 60 comprises a radio relay unit 63 and a central control unit70.

The radio relay unit 63 processes a radio signal received from the robotcleaner 10 and transmits the processed signal to the central controlunit 70 by wire, and then wirelessly sends a signal received from thecentral control unit 70 to the robot cleaner 10 through an antenna 62.

The central control unit 70 is constructed with a conventional computerof which one example is shown in FIG. 5. Referring to FIG. 5, thecentral control unit 70 comprises a CPU 71, a ROM 72, a RAM 73, adisplay 74, an input device 75, a memory 76 and a communication device77.

The memory 76 is provided with a robot cleaner driver 76 a forprocessing a signal from the robot cleaner 10.

Upon being operated, the robot cleaner driver 76 a provides a menu atthe display 74 for setting up the control of the robot cleaner 10, andprocesses a menu item, selected by a user through the input device 75,to be performed by the robot cleaner 10. Preferably, the menu mayinclude a command for performing cleaning work and/or security work asprimary classifications. The menu may further provide sub-selectionmenus for each primary classification such as a target area selectionlist and methods to be used for cleaning.

The robot cleaner driver 76 a controls the robot cleaner 10 so as torecognize the current position of the robot cleaner 10 by comparingposition information of special features or marks for recognition in acurrent upper image with the position information of the specialfeatures and marks for recognition stored in memory, and controls thedriving unit 20 corresponding to a target driving path from therecognized position. The robot cleaner driver 76 a further calculatesany driving error by using the driving distance and direction calculatedfrom the received image of the floor and the current position recognizedby comparing the currently received upper image with the previouslyphotographed upper images stored in the memory 76, and controls thedriving unit 20 to track the target driving path by compensating for thecalculated driving error.

The control unit 40 of the robot cleaner 10 controls the driving unit 20in response to the control signal received from the radio relay unit 63,and thus the operational load on the internal processor for processingthe images in order to recognize the position and to arrange the drivingpath is diminished significantly. The control unit 40 further transmitsthe upper image and the image of the floor photographed regularly in acycle while driving the robot cleaner 10 to the central control unit 70through the radio relay unit 63.

Hereinafter, a method for controlling the robot cleaner 10 by thecontrol unit 40 will be described in detail with reference to FIG. 6.

First, the control unit 40 decides whether a work command has beenreceived, S100.

When the work command is received, the control unit 40 determines thecurrent position of the robot cleaner 10 by using the upper images ofthe ceiling photographed by the upward-looking camera 30, and calculatesa driving path to move to a target position, which is a work area orwork path, corresponding to the received work command, S110.

The control unit 40 then photographs images of the floor by thedownward-looking camera 50 and stores the photographed floor images,S120.

Consequently, the control unit 40 drives the robot cleaner 10 along thecalculated driving path, S130.

The control unit 40 calculates a driving distance and direction bycomparing the current image of the floor with the image of the floorphotographed right before among the continuously photographed images bythe downward-looking camera 50, S140.

Thereafter, the control unit 40 analyzes a current driving path of therobot cleaner 10 to decide whether the current driving path agrees withthe calculated driving path, and decide whether the current driving pathrequires arranging, S150.

When it is decided at step S150 that the current driving path of therobot cleaner 10 requires arranging or correction, the control unit 40arranges or corrects the current driving path by using the analyzedinformation at steps S150, S160.

Next, the control unit 40 decides whether the work is completed, S170.The work here refers to work performed by driving the robot cleaner 10,for example, moving of the robot cleaner 10 to a target area or cleaningwork performed by driving the robot cleaner 10 along a driving path. Ifthe work is not completed, the control unit 40 repeats steps S130 toS170 until the work is completed, as shown by the loop.

As described above, when the driving distance and direction of the robotcleaner are determined by using the images of the floor photographed bythe downward-looking camera according to the invention, no error may beproduced even with a slip of the wheels of the driving unit or anirregularity in the floor, which may be produced in the prior art byusing the encoder. Therefore, the robot cleaner can efficiently performthe commanded work.

While the invention has been shown and described with reference tocertain preferred embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and detail may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

The foregoing embodiments and advantages are merely exemplary and arenot to be construed as limiting the present invention. The presentteaching can be readily applied to other types of apparatus. Thedescription of the present invention is intended to be illustrative, andnot to limit the scope of the claims. Many alternatives, modifications,and variations will become apparent to those skilled in the art. In theclaims, means-plus-function clauses are intended to cover the structuresdescribed herein as performing the recited function and not onlystructural equivalents but also equivalent structures.

1. A robot cleaner for performing a working operation while moving abouta floor, comprising: a main body; a driving unit for driving a pluralityof wheels disposed on a bottom portion of the main body; adownward-looking camera disposed among the wheels on the bottom portionof the main body for photographing images of the floor perpendicular toa direction of driving the robot cleaner; and a control unit forrecognizing the driving distance and direction of the wheels bycomparing current image information of the floor photographed by thedownward-looking camera with image information of the floor previouslymemorized by the downward-looking camera, and for controlling thedriving unit corresponding to a target work by using the recognizeddistance and direction of the wheels.
 2. The robot cleaner according toclaim 1, wherein the downward-looking camera photographs images of thefloor at a rate of 1500 times per second.
 3. The robot cleaner accordingto claim 2 further comprising an illuminator disposed on the bottomportion of the main body for illuminating an area photographed by thedownward-looking camera to render it brighter than surrounding areas. 4.A robot cleaner for performing a working operation while moving about afloor, comprising: a main body; a driving unit for driving a pluralityof wheels disposed on a bottom portion of the main body; adownward-looking camera disposed among the wheels on the bottom of themain body for photographing images of the floor perpendicular to adirection of driving the robot cleaner; an upward-looking cameradisposed on a top of the main body for photographing images of a ceilingperpendicular to the driving direction; and a control unit forrecognizing a position of the robot cleaner by using image informationof the ceiling photographed by the upward-looking camera and forrecognizing a driving distance and direction of the wheels by comparingcurrent image information of the floor photographed by thedownward-looking camera with image information of the floor previouslymemorized by the downward-looking camera, and further for controllingthe driving unit corresponding to the targeted work by using therecognized position, distance end direction.
 5. The robot cleaneraccording to claim 4, wherein the downward-looking camera photographsimages of the floor at a rate of 1500 time per second.
 6. The robotcleaner according to claim 5 further comprising an illuminator disposedon the bottom portion of the main body for illuminating an areaphotographed by the downward-looking camera so as to render it brighterthan surrounding areas.
 7. A robot cleaning system comprising: a robotcleaner including: a main body, a driving unit for driving a pluralityof wheels disposed on a bottom of the main body, and an upward cameradisposed on a top of the main body for photographing images of a cellingperpendicular to a direction of driving the robot cleaner; and a remotecontrol unit for communicating wirelessly with the robot cleaner,wherein the robot cleaner further include, a downward camera disposedamong the wheels on the bottom of the main body for continuouslyphotographing images of the floor perpendicular to the drivingdirection, and the remote control unit recognizes a driving distance anddirection of the wheels by comparing current image information of thefloor photographed by the downward camera with image information of thefloor previously memorized by the downward camera and controls thedriving unit corresponding to a target work by using the recognizeddistance and direction of the wheels.
 8. The robot cleaning systemaccording to claim 7, wherein the downward-looking camera photographsimages of the floor at a rate of 1500 times per a second.
 9. The robotcleaning system according to claim 8 further comprising an illuminatordisposed on the bottom portion of the main body for illuminating an areaphotographed by the downward-looking camera brighter than surroundingareas.
 10. A method for controlling a robot cleaner having a downwardcamera, comprising the steps of: calculating a driving path to a targetarea corresponding to a work, upon receiving a work command; storingimages of a floor photographed by the downward-looking camera; drivingthe robot cleaner along the calculated driving path; and comparing thecurrent image of the floor photographed by the downward-looking camerawith the stored images to calculate a driving distance and direction,and thereafter correcting the driving path.